Liquid crystal display device

Abstract

An object of the present invention is to provide a small-sized active matrix type liquid crystal display device that may achieve large-sized display, high precision, high resolution and multi-gray scales. According to the present invention, gray scale display is performed by combining time ratio gray scale and voltage gray scale in a liquid crystal display device which performs display in OCB mode. In doing so, one frame is divided into subframes corresponding to the number of bit for the time ratio gray scale. Initialize voltage is applied onto the liquid crystal upon display of a subframe.

What is claimed is: 
     
       1. A display device comprising:
 a semiconductor layer comprising a channel formation region; 
 a first insulating film over the semiconductor layer; 
 a second insulating film over and in contact with the first insulating film; and 
 a pixel electrode over the second insulating film, the pixel electrode being electrically connected to the semiconductor layer, 
 wherein the pixel electrode is a single layer in contact with a side surface of the first insulating film, a top surface of the first insulating film, a side surface of the second insulating film, and a top surface of the second insulating film. 
 
     
     
       2. The display device according to  claim 1 , wherein the semiconductor layer comprises silicon. 
     
     
       3. The display device according to  claim 1 , further comprising:
 a gate electrode over the semiconductor layer. 
 
     
     
       4. The display device according to  claim 1 , wherein the display device is a liquid crystal display device. 
     
     
       5. A display device comprising:
 a semiconductor layer comprising a channel formation region; 
 a first insulating film over the semiconductor layer; 
 a second insulating film over and in contact with the first insulating film; and 
 a pixel electrode over the second insulating film, the pixel electrode being electrically connected to the semiconductor layer, 
 wherein the pixel electrode is a single layer in contact with a side surface of the first insulating film, a top surface of the first insulating film, a side surface of the second insulating film, and a top surface of the second insulating film, and 
 wherein the first insulating film and the second insulating film comprise different materials. 
 
     
     
       6. The display device according to  claim 5 , wherein the semiconductor layer comprises silicon. 
     
     
       7. The display device according to  claim 5 , further comprising:
 a gate electrode over the semiconductor layer. 
 
     
     
       8. The display device according to  claim 5 , wherein the display device is a liquid crystal display device. 
     
     
       9. The display device according to  claim 5 ,
 wherein the first insulating film is an organic layer, and 
 wherein the second insulating film is a silicon nitride layer. 
 
     
     
       10. A display device comprising:
 a semiconductor layer comprising a channel formation region; 
 an interlayer insulating film over the semiconductor layer; 
 a first conductive film over the interlayer insulating film, the first conductive film being electrically connected to the semiconductor layer; 
 a second conductive film over the interlayer insulating film, the second conductive film being electrically connected to the semiconductor layer; 
 a first insulating film over the semiconductor layer, the first conductive film, the second conductive film; 
 a third conductive film over the first insulating film; 
 a second insulating film over and in contact with the first insulating film and the third conductive film; and 
 a pixel electrode over the second insulating film, the pixel electrode being electrically connected to the semiconductor layer through the second conductive film, 
 wherein the pixel electrode is in contact with a side surface of the first insulating film, a top surface of the first insulating film, a side surface of the second insulating film, and a top surface of the second insulating film, 
 wherein the first insulating film is an organic layer, and 
 wherein the second insulating film is a silicon nitride layer. 
 
     
     
       11. The display device according to  claim 10 , wherein the semiconductor layer comprises silicon. 
     
     
       12. The display device according to  claim 10 , further comprising:
 a gate electrode over the semiconductor layer. 
 
     
     
       13. The display device according to  claim 10 , wherein the display device is a liquid crystal display device. 
     
     
       14. The display device according to  claim 10 , wherein a storage capacitor is formed by the third conductive film, the second insulating film, and the pixel electrode. 
     
     
       15. The display device according to  claim 10 , wherein the third conductive film is a light-shielding film. 
     
     
       16. The display device according to  claim 10 , wherein the pixel electrode is a single layer. 
     
     
       17. A display device comprising:
 a semiconductor layer comprising a channel formation region; 
 an interlayer insulating film over the semiconductor layer; 
 a first conductive film over the interlayer insulating film, the first conductive film being electrically connected to the semiconductor layer; 
 a second conductive film over the interlayer insulating film, the second conductive film being electrically connected to the semiconductor layer; 
 a first insulating film over the semiconductor layer, the first conductive film, the second conductive film; 
 a third conductive film over the first insulating film; 
 a second insulating film over and in contact with the first insulating film and the third conductive film; and 
 a pixel electrode over the second insulating film, the pixel electrode being electrically connected to the semiconductor layer through the second conductive film, 
 wherein the pixel electrode is in contact with a side surface of the first insulating film, a top surface of the first insulating film, a side surface of the second insulating film, and a top surface of the second insulating film, 
 wherein the first insulating film is an organic layer, 
 wherein the second insulating film is a silicon nitride layer, 
 wherein the pixel electrode has a depressed portion overlapping with a contact hole of the first insulating film, 
 wherein a slope of the side surface of the second insulating film is steeper than a slope of the side surface of the first insulating film, and 
 wherein the display device is a liquid crystal display device. 
 
     
     
       18. The display device according to  claim 17 , wherein the semiconductor layer comprises silicon. 
     
     
       19. The display device according to  claim 17 , further comprising:
 a gate electrode over the semiconductor layer. 
 
     
     
       20. The display device according to  claim 17 , wherein a storage capacitor is formed by the third conductive film, the second insulating film, and the pixel electrode. 
     
     
       21. The display device according to  claim 17 , wherein the third conductive film is a light-shielding film. 
     
     
       22. The display device according to  claim 17 , wherein the pixel electrode is a single layer.